This invention relates to the testing of materials, and more particularly to the monitoring of the degradation of lubricant materials.
The evaluation of lubricant stability is very important for designers, producers, and users of lubricants. Perhaps the greatest interest is focused on evaluating the stability of lubricants in an oxidizing environment since oxidative degradation is the primary cause of lubricant failure. Typically, a lubricant sample whose volume may lie in the range of 10 to 1,OOO ml) is placed in a temperature controlled oven (heated between 50.degree. and 300.degree. C.) and air or oxygen is bubbled through the sample at a constant flow rate. Samples are taken from the apparatus at regular intervals and analyses are performed to measure such things as viscosity change, acidity increase or peroxide formation. In most tests, an antioxidant material is added to the lubricant, and the rate at which the antioxidant disappears is measured and related to lubricant stability. A popular alternative method for oxidation testing of lubricants requires a closed "bomb" which is charged with oxygen gas and the lubricant. The rate at which the oxygen pressure drops is directly proportional to the extent of lubricant oxidation. This particular test requires elaborate apparatus and large lubricant samples. The previously mentioned techniques (i.e., viscosity, acidity, etc.) require large samples of lubricant along with periodic sampling and analysis of the test mixture (i.e., lots of manual labor). Clearly the existing techniques are inadequate if one is interested in using small sample sizes (e.g., 1 ml) or if automation of the evaluation process is desired.